Wait, are we talking about Michael Saylor and MicroStrategy? Because he sold a small portion of BTC to pay dividends. Whether you're talking about Saylor or not, yeah, Ponzi works like that. They need initial capital to pay the early users in the system until new users join and are able to pay the earlier users. And by then, the system runs itself until no more fresh money is injected into the system.
However, if you think what Saylor did by selling BTC to pay dividends is a Ponzi scheme, I don't agree with you. For me, it's just like property investors who do the loop. They build properties, then use them as collateral to get loans, then use the money to buy or build more properties. There's also interest they should pay to the bank, "the investors". As long as the property price rises, it would work well. But if not, the pressure becomes bigger from the negative capital gain and the interest that still needs to be paid. IMO, this is not a Ponzi scheme. It's just a system that relies heavily on market trust and the BTC price itself.
A lot of people called it ponzi because the yield distributed isn't sustaining, coming from new buyers and expecting 30% CAGR from Bitcoin they bought.
They are paying dividend from their cash reserve, not from a productive capital and the fact that they give out above average yield is concerning.
Whether you call it ponzi or not, one fact stands, the entire thing isn't sustainable.